Method for cracking high boiling hydrocarbons



5 Sheets-Sheet 1 BOL Dvd D NIDOOOHd NOGHVD INVENTR. PAUL T. ATTERIDG ATTORNEY AGENT 5 Sheets-Sheet 2 o Ema ooo. ns.

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METHOD FDR caAcxING HIGH BDILING HYDRDCARBONS Filed Jan. 7, 1960 5 Sheets-Sheet 4 loo o I M=IOOO Ppm DAY 7 TIME TO REACH MAXIMUM CPF l -VERSUS- REPLACEMENT RATE 0'7 (PARAMETER: METALS FEED RATE (aAsls cATALYs'U) 0.00| 0.002 0.004 0,007 O Ol 0.02 0.04 0.07 OJ 0.2 0.4 0.7 1.0

DAILY FRAcTuoNAL REPLACEMENT RATE@ TIME RQUIRED TO REACH MAXIMUM CPF, DAYS N INVENTOR. PAUL T. ATTERIDG ATTORNEY 'AGENT June 4, 1963 P. T. ATTERIDG 3,092,558

METHOD FUR cRAcxING HIGH BOILING HYnRocARBoNs Filed Jan. 7, 1960 5 Sheets-Sheet 5 FIG. 5

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ULTIMATE 'DAILY FRACTIONAL REPLACEMENT RATE IN1/wrox. PAUL T. ATTERIDG BY #LZM.

ATTORNEY AGENT United States Patent O 3,092,568 METHOD FOR CRACKING HIGH BOILING HYDROCARBONS Paul T. Atteridg, Upper Montclair, NJ., assignor to M. W. Kellogg Company, Jersey City, NJ., a corporation of Delaware Filed Jan. 7, 1960, Ser. No. 1,051 9 Claims. (Cl. 208-113) This invention relates to a method for treating hydrocarbons containing metal contaminants. More particularly, the invention relates to a method of converting relatively heavy or high-boiling hydrocarbons including topped or reduced crudes or similar heavy hydrocarbons to gasoline boiling range products and higher boiling fractions substantially free of metal contaminants which are suitable as feeds for further conversion to desired products including gasoline boiling range products of high quality.

Control over the quantity of fuel oil produced and improvements in gasoline quality and quantity has been, for many years, a serious problem of the petroleum industry. `ln some areas the demand for gasoline and distillate fuel has considerably increased, whereas the de mand for fuel oil has actually decreased. Reduction of fuel oil yields has been accomplished by a variety of processes including vacuum distillation, visbreaking, coking, solvent decarbonizing or a combination of these techniques. Whenever catalytic processes have been considered for further reduction or elimination of fuel oil products one major stumbling block has been encountered which is directed to the metal contaminants in these feeds and their deleterious effect on product distribution, as well as economic considerations. Accordingly, a major problem associated with the petroleum industry is treating high-boiling hydrocarbons such as a total crude or portions thereof referred :to as residual oils or reduced crudes which contain appreciable quantities of metal contaminants sometimes referred to as organic metal contaminants including nickel, vanadium, copper, chromium an-d iron.

Accordingly, it is a principal object of this invention to provide an improved process or method for converting high-boiling hydrocarbons containing metal contaminants to produce high quality gasoline products, as Well as higher boiling distillate fractions substantially free of metal contaminants which may be subjected to further cracking to produce high yields of high quality gasoline.

Other objects and advantages of the improved process of this invention will `become obvious from the following discussion.

In treating high-boiling hydrocarbon feed materials including total crudes, residual oils, topped and reduced crudes in accordance with one embodiment of this invention, the feed is preheated to a temperature in the range of from about 200 to about 800 F. and thereafter the preheated feed, either as a liquid or partially vaporized, is passed in contact with a sufficient quantity of hot finely divided solid particulate material to provide the resulting mixture with a sufficiently elevated temperature to accomplish the desired degree of conversion or cracking of the feed. While the ratio of finely divided particulate material to oil feed may be as low as 2:1, it is prefererd that the ratio be in the range of from about 5 to about 20:1. Accordingly, a suicient amount of hot finely divided solid particulate material is employed to supply relatively large amounts of heat required to convert the hydrocarbon feed in the endothermic cracking operation. Another very important reason for using a relatively large amount of contact material is to provide intimate contact of porphyrins in the feed and t0 3,092,568 Patented June 4, 1963 ICC effect their resultant decomposition with the contact material.

ln another embodiment, the present invention is based on the discovery that the high-boiling hydrocarbons delined herein and containing metal contaminants may be converted to high yields of desired products substantially free of metal contaminants by cracking in the presence of a cracking catalyst under conditions whereby the carbon producing factor of the catalyst is maintained within a range of from about 2 to about 8, preferably from about 3 to about 6, by continuously adding fresh cracking catalyst to the system at a rate which is dependent in part upon the level of metal contaminants (in part per million) in the feed. More specically, the invention is directed to cracking relatively high-boiling hydrocarbons containing metal contaminants in the presence of a uidized catalytic material under conditions to maintain a relatively high catalyst replacement rate initially or during start-up of the process and thereafter reducing the replacement rate to a lower value consistent with maintaining desired economic operating conditions, as well as maintaining the catalyst at a desired equilibrium condition.

In accordance with one embodiment of this invention, the conversion of the high-boiling hydrocarbons containing relatively large quantities of metal contaminants in the range of from about 5 to about 5,000 parts per million (p.p.m.), more usually from about l0 to about 500 ppm. is accomplished in the presence of a relatively large amount of synthetic and/or naturally occurring cracking catalyst, either alone or in admixture. It is also contemplated employing the cracking catalyst in admiXture with finely divided inert solid material under conditions to control conversion of the hydrocarbon within a desired range and maintain the catalyst carbon producing factor (CPF) within the range herein defined.

When employing nely divided inert solid material in conjunction with the catalytic material, the inert solids may be of the same or different particle size and may be selected from the group comprising coke, pumice, kieselguhr, clay, spent cracking catalyst, sand, or any other suitable finely divided solid material, which may be partially or completely uidized with the catalyst in the reactor by the gasiform or vaporous materials introduced thereto. In addition to the above, it is contemplated within the scope of this invention to employ an absorptive material which may or may not have catalytic activity but which has a relatively high surface area and has a relatively low resistance to attrition such that it is being continuously eroded and lost from the process. As hereinbefore discussed, naturally occurring cracking catalyst may be combined with synthetic cracking catalyst and employed in a ratio such that the maior portion of the catalyst mixture comprises the naturally occurring cracking catalyst.

During conversion of the residual oils, relatively large amounts of Carbonaceous material, as well as metal contaminants, are deposited on the catalyst. Carbonaceous material is removed from the catalyst by burning in the presence of air or an oxygen-containing gas in a suitable regeneration zone such that during combustion of the carbonaceous deposits the finely divided solid material is heated to an elevated temperature suitable for recycling to the conversion zone. Generally, during combustion of the Carbonaceous material in the regeneration zone the finely divided solids will be heated to an elevated temperature in the range of from about 1050 F. to about 1400 F., preferably about 1150 F. to about 1250 F.

lt is well known at this stage of the art that lluid type operations afford the greatest advantages with respect to heat transfer, temperature control, economy and continuity of operation. In the conversion of residual oils and reduced crudes to lower boiling hydrocarbons in a uid-type operation, it is desirable to employ a gasiform diluent material with the oil feed in sufficient amounts to facilitate vaplorization and/or atomization of the feed, thereby breaking up the high boiling feed into relatively small droplets for intimate contact with the finely divided solid material. In addition, the use of gasiform diluent such as steam with the high-boiling oil feed desirably reduces the partial pressure of the feed during conversion to within the range of from about 1 to about 15 p.s.i.a. Accordingly, intimate contact of the hydrocarbon feed with the catalyst recovery of conversion products and iluidization of the finely divided contact material is greatly enhanced by the use of a feed diluent by reducing the tendency of hydrocarbon feed-catalyst agglomerants forming in the tiuid bed. Suitable feed diluents which may be used in the method of this invention include steam, lowboiling gaseous hydrocarbons, hydrogen-rich product gases, nitrogen, flue gases, etc.

Hydrocarbon feeds suitable for cracking operations usually contain metal contaminants in varying proportions, depending in part upon the source of the hydrocarbon feed. Generally the metal contaminants found in various hydrocarbon crudes will be found in the range of from about 2 to about 3000 ppm., with the highest concentration being found in the residual oils. By metal contaminants it is intended to include those metals which are found in most crude oils, such as vanadium, nickel, iron, copper, chromium, etc., which are concentrated `upon distillation into the higher boiling distillate and residue fractions, generally known as the reduced crude or residual oil fraction. In residual oils, the metal contaminants may be further concentrated in the range of from about 5 to about 5000 p.p.m. When cracking these metal contaminated residual oils, the metal contaminants collect on and even become embedded in the catalyst, thereby poisoning the catalyst. The thus poisoned catalyst tends to increase the production of coke and gaseous materials.

The hydrocarbon feed materials which may be effectively processed in accordance with this invention include total crudes, residual oils, topped and reduced crudes wherein the feed may constitute from about l percent to about 100 percent, more usually from about l0 percent to about 65 percent of the total crude, and generally may have a gravity in the range of from about 5 to about 25 API. As hereinbefore indicated, residual oils may be readily used in uid operations without taking extreme measures to insure complete vaporation or atomization of the feed material by using a gasiform feed diluent and a sufficient quantity of catalyst with the feed to form a relatively dry mixture. Generally, the residual oils to be processed in accordance with this invention will contain components boiling above about 700 F. in an amount ranging from about 30 percent to about 100 percent and will contain compounds of a highly asphaltic nature, sulfur-containing compounds 'or metal organic compounds such as porphyrins, salts of metals, which poison the catalyst and have an adverse effect upon the cracking catalyst activity and carbon producing factor. In general, the carbon residue of the residual oil is at least about 1 percent by weight and more usually will be in the range of from about 2 percent to about 30 percent by weight, with the sulfur content depending upon the source of the crude varying in the range of from about 0.5 to about 5 percent by weight.

ln a catalytic cracking operation the conversion level serves to describe the severity of operation. The severity desired may be obtained by regulating the temperature, the amount of gaseous diluent, the time of contact and/ or space velocity, the catalyst to oil ratio and the level of catalyst activity. It is the relative effect of these variables and particularly the catalyst addition rate to maintain the catalyst carbon producing factor within a desired range with which I am particularly interested in this invention. One method to describe severity in a cracking operation is by reference to the conversion level, which is defined as:

wherein Vf is the volume of feed and Vp is the volume of product boiling above 400 F. For the cracking operation contemplated by this invention, the conversion level is desirably maintained above about 20 percent and preferably from about 30 to about 55 percent and may even be from about 50 percent to about 70 percent in a recycle operation.

It is generally known that in commercial cracking operations, as known today, such as gas oil cracking operations, finely divided catalyst is continuously lost from the system as lines, which are recovered in part from the decanted oil of the fractionating tower and the recovered fines are then returned to the reactor in the form of a slurry. In addition to this catalyst loss, there is a loss of catalyst fines in the regenerator flue gases, which loss is minimized through the use of rather elaborate cyclone separator equipment for the recovery of these catalyst lines. However, in such operations, the recovered fines are returned to the process and the catalyst loss is minimized such that only a relatively small fraction of the catalyst inventory is loss from the process and must be replaced by make-up catalyst. Generally, this catalyst loss in gas oil cracking operations amounts to less than about .5 pound of catalyst per barrel of oil feed, and most usually is less than this value, of the order of about .3 pound of catalyst per barrel of oil feed, or less. This invention is concerned, however, with replacing used catalyst with fresh catalyst at a rate generally above about .5 pound of catalyst per barrel of oil feed without return of the thus replaced and used catalyst to the system.

The cracking of high-boiling hydrocarbons such as residual oils, topped and reduced crudes is accomplished by this invention at a temperature below about 1000 F., generally in the range of from about 850 F. to about l000 F., and preferably from about 900 F. to about 950 F., using a pressure in the range of from about atmospheric to about 50 p.s.i.g., and preferably from about 5 to about l5 p.s.i.g. Under these conditions of operation sufticient gasiform diluent material such as steam is used with the hydrocarbon feed to maintain the partial pressure of the feed below about l5 p.s.i.a., usually below about l0 p.s.i.a., depending upon the residual oil being treated and preferably from about 2 to about 8 p.s.i.a. The relationship of the oil feed rate to the amount of finely divided solid material which is present in the reaction zone is known as the weight space velocity and is measured as the pounds of oil feed per hour per pound of contact material in the reaction zone. Generally cracking of the contaminated high-boiling oil feeds herein contemplated is effected at weight space velocities in the range of from about l to about 10, and preferably from about 3 to about 6. When employing an inert finely divided solid material diluent with the catalyst as hereinbefore indicated, it is contemplated employing from about 5 percent to about 75 percent inerts and preferably from about 25 percent to about 50 percent inerts with the active cracking catalyst. It is to be understood as herein discussed that a synthetically prepared or naturally occurring catalyst substantially free of inert material may also be employed in accordance with this invention.

Applicants efforts to resolve the problems associated with the catalytic cracking of high-boiling oils, particularly residual oils, topped and reduced crudes contarninated with metals was initiated by treating a suitable cracking catalyst with various reagent metal salt solutions and determining their iniiuence on the catalyst carbon producing factor. It was determined in an early part of this investigation based on the product distribution obtained with catalysts of different carbon factors Percent conv.

that the catalyst carbon factor should be maintained in the range of from about 1.5 to about 10 and preferably 1n the range of from about 2 to about 6 or 8. By carbon producing factor I mean the ratio of the carbon produced by the catalyst relative to the carbon yields from a standard catalyst employed under the same con version conditions. The test procedure for determining the carbon producing factor (CPF) involved contacting 50 grams of powdered catalyst for l0 minutes with `a Standard Mid-Continent gas oil at 925 F., l atmospheric pressure and a space velocity of 2.3 w./hr./w. It was ound in this investigation `that iron as iron oxide physically admixed with catalyst had little or no effect, but that catalyst treated with iron, nickel, copper and vanadium salt solutions seriously hurt catalyst CPF after calcining. By calcining we mean heating the catalyst in air atmosphere at temperatures in the range of from about 1000 F. to about l400 F. for periods of from about one to about four hours. Vanadium was found to be considerably less deleterious than copper and nickel with iron intermediate between nickel and vanadium. Relative to nickel, the effects were Ni/Fc/V=1/0.55/0.091

with copper having substantially the same effects as nickel. The term nickel equivalents used herein refers to the total metals content of the catalyst expressed as equivalent nickel (p.p.m.) parts per million using the above effects ratio.

The problems associated with the catalytic cracking of high-boiling hydrocarbon feed material containing metal contaminants were investigated by determining the effect of metals content on carbon factor and determining the carbon factor when the equiiibrium metals content and activity had been attained. This work showed that the carbon factor of a catalyst depended, not only on the metals content, but also on the ability of the catalyst to deactivate: fresh catalysts, which lose a large portion of their activity in a relatively short time, have lower canbon factors (for a given metals concentration) than used catalysts whose activities are low but stable. From these ndings, suitable equations were developed which could fbe relied upon for predicting the catalyst carbon producing factor in reduced crude cracking when (l) starting with fresh catalyst and replacing with fresh catalyst, (2) starting with used catalyst and replacing with used catalyst, and (3) starting with used catalyst and replacing with fresh catalyst. It was recognized that (3) would be the most frequently encountered case, since most refiners would have an existing inventory of used catalyst, or would prefer to use it to keep within gas-handling limitations. While such a situation or method of operation would be identical at equilibrium conditions with the situation in which lone starts with fresh catalyst and replaces with fresh catalyst, a maximum carbon producing factor would be attained shortly after commencing reduced crude cracking and would be higher than the equilibrium carbon producing factor. The extensive calculations employing the equations developed in this investigation have not been presented for purposes of simplification, however, the carbon producting factor (CPF) values obtained for various values of a and 0 at levels of M equal to 100, 400, 700 and 1000 ppm. per day are presented in Table I below. In the table, a is the catalyst replacement rate, fraction lof inventory per day; H is the time in days; and M is the metals feed rate, pounds per day per million pounds of catalyst (or ppm. basis catalyst per day).

TABLE I Carbon Factors in Reduced Crude Cracking {Tabulated at various levels of daily fractional replacement rate (a), metals feed rate (basis catalyst) (M), and time in days (0)] Time (6), in Days 4. 6. 7.7 8. S. 7. 1l. 14. 4 15. 15. 11. 9. 14. 18. 7 20. 2D. 15. 1Dv 17. 22. 2 24. 24. 18.

5. 6.0 6. 9. 10.9 ll. 12. 14.1 I4. 14. 16.6 16.

en usan: huawei: @Hr-cn 00006105 wacnlooowmw come@ www catalyst (M), and time lx1 days (6)] a M Time in Days 0. 1.63 1.67 1.63 1.62 1.53 1.38 1.29 1.26 1.25 1.25 0. 1. s2 1.99 2.1 2.6 1.92 1.74 1.59 1.54 1.52 1. 52 o. 2.1 2.2 2.3 2.3 2.2 1.96 1.79 1.72 1.69 1.69 0. 2.2 2.4 2.5 2.5 2.4 2.1 1.94 1.83 1.83 1.83 1. 1.57 1.57 1.52 1.39 1.25 1.16 1.14 1.13 1.13 1.13 I. 1.30 1.32 1.76 1.64 1.47 1.32 1.23 1.27 1.27 1.27 1. 1.95 2.o 1.32 1.84 1.60 1.43 1.37 1.36 1.36 1.36 1. 2.1 2.1 2.1 1.94 1.71 1.51 1.44 1.43 1.43 1.43

FIGURE 1 presented herewith is a plot of the data per barrel at equilibrium is desirable. In this example presented in Table I wherein the carbon producing factor the unit is to be started up with a charge of used catalyst. is plotted against 0, the time in days, for various values What is to be determined is (l) the ultimate canbon facof a and M. tor, (2) the initial replacement rate in order that the FIGURE 2 is a plot of the equilibrium carbon factor 25 carbon factor does not exceed its ultimate value, and for different daily fractional replacement rates a and (3) how long this initial replacement rate must be used. the same four levels of metals feed rate M From The metal feed rate (M) will be FIGURE 2 the equilibrium carbon factor for the different N- E b d f d d d -t metals feed rates is readily determinable for the different 1 qmv gai; gli e ens! y daily fractional replacement rates a.

FIGURE 3 is a plot of the maximum carbon producing :www factors for different daily fractional catalyst replacement 200X2000 raies dePendIl-UP0n the metals freed fate or 400 p.p.m. (basis catalyst) per day. At equilibrium,

FlGURE 4 1S a Plot of the Ume l'equled l (lays to 35 the catalyst replacement rate fraction of inventory per day reach maximum carbon producing factor for the different (a") will be daily fractional replacement rates a at different metals feed rates. M

FIGURE 5 was obtained by cross-plotting FIGURES 200 2000 2, 3 and 4 to show the magnitude and duration of initial 40 or 0 025 FIGURE 2 shows that for a fractional re, @Placement Tate VS Ultimate replacement fato for the placement rate of 0.025 the ultimate carbon factor will dItl'erent metals feed rates. be 5 4.

lt lsfo be "oleo from a sllld of FIGURE l lllal aflel' As herein discussed, a carbon factor of about 5.4 falls a felallvoly Sllol't lll'lle a maxlmllm carbo factor ls ol" within applicants preferred range and is a desired contamed, reflecting a balance between (l) impregnation of dition under whidh to operate. From FIGURE 5 it is Sed catalyst Wllll melals from the feed and (2) ellll'lllla' now determined that for a daily fractional replacement tion of the used catalyst and replacement with more rapIdrate of 0'025 the initial replacement rate for example ly leactlvallllg (and lloll lower o arboll facto?) added at start-up of the process will be 0.043. From this value catalyst. As time increases the initial catalyst Inventory of 0 043 the replacement rate il1 terms of l:minds of 1s completely purged from the systemand the equ1l1br1um 50 catalyst per barrel of feed iS readily determined; that carbon factor is approached asymptoucally, with the magis nitude of the equilibrium carbon factor being determined l from the plot of FIGURE 2. The maximum carbon pro- 0.0L 3X 200X 2000= ducing factors readable from FIGURE 1 (and from simi- 10,000 1'7 pounds can/banal feed lar plots of Glher levels of a and M aine hsted-m must be used. As shown by FIGURE 5 this higher rate Table 2 and are plotted 1n FIGURE 3. The time elapsmg must be used for about the r t 17 d f o ti n before the maxima are reached are plotted in FIGURE 4. (this value fail between 10 sd 20 ay Oi pei?) go By @ross-planing FIGURES 2, 3 and 4, FIGURE s was th Sm af than i a 1c el constructed to Show: on te eureyd ire tei; 1Ee oatfli yst repbaccnient fret (1) What replacement rate must be used initially in 6o gatiirie fengnedpe(cfilederrriof that order that the maximum carbon producing factor just y y a ed 1s, after this time has elapsed, the reiiner may slowly equals the equIlIbrIum carbon factor, and d h. i t .i d u h h d (2) How long this rate must be used before the maxire uca 1S rep amen ra uml gra a y It as mac e l lb./bbl.' from the 17th day on a constant carbon factor mum carbon factor 1s reached.

of 5.4 would thus be maintained. EXAMPLE Note that if l pound per barrel were used from the As a specific example of the improved method of this start, a maximum carbon factor of 7.0 (FIGURE 3) invention and to demonstrate how the figures and data would be reached after 28 days (FIGURE 4)--a distinctly presented herein are to be used, the following example is unattractive level in a unit designed for 5.4. presented. A catalytic cracking unit designed to contain Having thus given a general description of this inven- 200 tons of catalyst and to treat 10,000 b.p.d. of a tion and specic examples thereof, itis to be understood reduced crude Weighing 310 pounds per barrel and conthat many modifications may be made thereto without taining 52 parts per million of nickel equivalent is to departing from the spirit thereof. be operated. An economic analysis of the proposed op- I claim: eration indicates that make-up catalyst should be fresh l. A method for converting high-boiling hydrocarbons synthetic catalyst and that a replacement rate of 1 pound 75 containing metal contaminants to lower boiling hydrocarbons which comprises passing a high-boiling hydrocarbon feed in contact with a cracking catalyst maintained in a iluidized condition, (a) replacing catalyst when the hydrocarbon feed is initially supplied to the process at a predetermined initial fractional replacement rate of catalyst per day for a predetermined initial time, (b) thereafter reducing the catalyst replacement rate to another lower predetermined ultimate rate and carrying out the cracking process at said lower rate, the ultimate rate for step (b) being within the range of 0.004 to 0.2 and the catalyst replacement rate and time of use for step (a) being in accordance with the correlation of the ultimate catalyst replacement rate and metals feed rate according to the curves of FIGURE 5.

2. A method for converting high-boiling hydrocarbons containing metal contaminants to lower boiling hydrocarbons which comprises passing a high boiling hydrocarbon feed in contact with a cracking catalyst maintained in a uidized condition, (a) replacing catalyst when the hydrocarbon feed is initially supplied to the process at a predetermined initial fractional replacement rate of catalyst per day for a predetermined initial time, (b) thereafter reducing the catalyst replacement rate to another lower predetermined ultimate rate and carrying out the cracking process at said lower rate, the ultimate rate for step (b) being within the range of 0.004 to 0.2, and the initial catalyst replacement nate for step (a) being correlated with the ultimate catalyst replacement rate for a given time and metals feed rate in accordance with FIG- URE 3. The method of claim 2 wherein the ultimate catalyst replacement rate is correlated with the catalyst carbon producing factor and the metals feed rate M according to FIGURE 2.

4. A method for cracking hydrocarbon feed materials including residual oils, topped and reduced crudes containing metal contaminants to lower boiling range materials which comprises cracking a hydrocarbon feed material containing metal contaminants in the presence of a cracking catalyst wherein the catalyst employed in the cracking step is initially replaced with a fresher catalyst at a higher catalyst replacement rate than the catalyst replacement rates are made for the metals feed rate in accordance with the correlations of FIGURE 2 and FIGURE 5.

5. The method of claim 4 wherein cracking of the hydrocarbon feed is effected in the presence of a mixture of synthetic and naturally occurring cracking catalyst.

6. The method of claim 4 wherein cracking of the hydrocarbon feed is effected in the presence of cracking catalyst containing a major portion of a relatively inert solid particulate material admixed therewith.

7. The method of claim 4 wherein cracking of the hydrocarbon feed is effected at a temperature in the range of from about 850 F. to about 1000 F. and in the presence of a sucient quantity of a relatively inert gaseous material to maintain the partial pressure of the hydrocarbon feed during contact with the catalyst within the range of from about 2 to about l0 p.s.i.a.

8. The method of claim 4 wherein the catalyst initially employed is used catalyst which is replaced with a fresh synthetic catalyst.

9. The method of claim 4 wherein conversion of the hydrocarbon feed is maintained within the range of from about 20 to about 55 percent.

References Cited in the file of this patent UNITED STATES PATENTS 2,290,845 Voorhees July 2l, 1942 2,421,616 Hemminger et al. June 3, 1947 2,690,991 Packie Oct. 5, 1954 2,903,414 Marisic et al Sept. 8, 1959 2,956,004 Conn et al Oct. 1l, 1960 OTHER REFERENCES Whitaker et al., Ind. & Eng. Chem., vol. 47, No. 10, October 1955, pages 2153 to 2157. (Copy in Patent Oihce Scientific Library.)

Johnson et al.: Ind. & Eng. Chem. vol. 49, No. 8, August 1957, pages 1255 to 1258. (Copy in Patent Office Scientific Library.) 

1. A METHOD FOR CONVERTING HIGH-BOILING HYDROCARBONS CONTAINING METAL CONTAMINANTS TO LOWER BOILING HYDROCARBONS WHICH COMPRISES PASSING A HIGH-BOILING HYDROCARBON FEED IN CONTACT WITH A CRACKING CATALYST MAINTAINED IN A FLUIDIZED CONDITION, (A) REPLACING CATALYST WHEN THE HYDROCARBON FEED IS INITIALLY SUPPLIED TO THE PROCESS AT A PREDETERMINED INITIAL FRACTIONAL REPLACEMENT RATE OF CATALYST PER DAY FOR A PREDETERMINED INITIAL TIME, (B) THEREAFTER REDUCING THE CATALYST REPLACEMENT RATE TO ANOTHER LOWER PREDETERMINED ULTIMATE RATE AND CARRYING OUT THE CRACKING PROCESS AT SAID LOWER RATE, THE ULTIMATE RATE FOR STEP (B) BEING WITHIN THE RANGE OF 0.004 TO 0.2 AND THE CATALYST REPLACEMENT RATE AND TIME OF USE FOR STEP (A) BEING IN ACCORDANCE WITH THE CORRELATION OF THE ULTIMATE CATALYST REPLACEMENT RATE AND METALS FEED RATE ACCORDING TO THE CURVES OF FIGURE
 5. 